In internal combustion engines, including diesel and gasoline engines, a fuel and air mixture is combusted in combustion cylinders. Reciprocating pistons in the combustion cylinders are moved between top dead center and bottom dead center positions by a crankshaft positioned below the cylinders in a crankcase. As each piston moves toward its top dead center position, it compresses the fuel and air mixture in the combustion chamber above the piston. The compressed mixture combusts and expands, driving the piston downward toward its bottom dead center position.
The exhaust gases of the engine are typically released from the combustion cylinders of the engine into the atmosphere through an exhaust stack or tailpipe. These exhaust gases, however, may contain a complex mixture of air pollutants generated as byproducts of the combustion process, and it may be desirable to reduce the amount of such pollutants being released into the atmosphere. Due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes utilizing an exhaust gas recirculation (EGR) system. EGR systems typically operate by recirculating a portion of the exhaust gas produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture may produce a lower combustion temperature and, subsequently, generate a reduced amount of regulated pollutants.
Instead of being exhausted from the engine, however, some of the combustion byproducts may enter into the crankcase by blowing past seal rings around the pistons, and may thus be referred to as “blow-by gases” or simply “blow-by.” Blow-by gases may contain contaminants normally found in exhaust gases, such as hydrocarbons (HC), carbon monoxide (CO), NOx, soot, and unburned or partially burned fuel. Because the crankcase is partially filled with lubricating oil, which is in contact with hot engine components, and agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor. In addition, the crankcase may contain a concentration of one or more gaseous constituents, such as oxygen contained in air within the crankcase.
As blow-by gases accumulate in the crankcase, the crankcase may be ventilated to remove the blow-by gases to relieve pressure in the crankcase, and to remove an amount of a gaseous constituent (e.g. oxygen) from the crankcase. Some systems vent the blow-by gases directly to the atmosphere. However, because the contaminants in blow-by gases can harm the environment, other crankcase ventilation options have been explored. For example, U.S. Pat. No. 7,159,386 to Opris (“Opris”) discloses a crankcase ventilation system for an internal combustion engine, whereby crankcase exhaust gases are routed to a main exhaust conduit extending from an engine exhaust manifold. In particular, crankcase exhaust gases merge with the main exhaust conduit downstream of a particulate trap disposed in the main exhaust conduit. According to Opris, because the pressure of the exhaust gases in the main exhaust conduit downstream from the particulate trap may be lower than the pressures within the crankcase of the engine, crankcase exhaust gases may flow from the crankcase to the main exhaust conduit without the aid of a pump.
The crankcase ventilation system described by Opris also includes an EGR system that may extract main exhaust gases from the main exhaust gas conduit, and direct the extracted main exhaust gases back to an air intake to be reintroduced into combustion chambers of the engine. The exhaust gases that flow through the EGR system disclosed by Opris, however, are not routed through the crankcase for crankcase ventilation.
As noted above, crankcase ventilation may be used to remove exhaust gas, along with one or more gaseous constituents, from the crankcase. Because oil droplets and oil vapor may accumulate in the crankcase during normal engine operation, oil vapor may be exhausted into the atmosphere during ventilation, contributing to exhaust emissions. While an oil filtering device, such as an oil separator, may be incorporated into a crankcase ventilation system to minimize oil vapor being emitted into the atmosphere, some oil vapors may still be exhausted into the atmosphere.
The disclosed engine system and method are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.